This invention relates to an interface apparatus and method and an image output apparatus having the interface apparatus and, more particularly to an interface apparatus for transmitting/receiving information with an external apparatus via a communication line, a method for negotiating for transmitting/receiving information between apparatuses, and an image output apparatus having the interface apparatus.
Generally, a printer and an information processing device are connected via a fixed type communication interface. In each device, an open-collector type interface circuit or totem-pole type interface circuit is fixedly provided, and it is impossible to select an interface circuit in accordance with the specification of communication destination device.
However, in a case where a device has only an open-collector type interface circuit, even if another device as a communication destination uses a totem-pole type interface, high-speed communication cannot be performed. In an open-collector type interface circuit, a transitional period where a signal level changes from a high level to a low level, and a transitional period where the signal level changes from the low level to a high level are greatly different. Especially, the transition of signal level from the low level to the high level is made very slowly.
In a case where the device has only a totem-pole type interface circuit, if the power of the communication destination device is turned off and the communication line is in short-circuit or in low-impedance status, overcurrent occurs, which consumes a large amount of electricity and may cause the interface circuit to generate heat.
There is a tendency of signal voltage swing to be complicated, since small signal voltage swing is used to increase communication speed or to save electricity. A device corresponding to only one signal voltage swing cannot handle communication with devices of various specifications. In many cases, the input characteristics of signals and the output characteristics of signals do not coincide with each other.
Further, even though the device can communicate with a high-performance device, if the device cannot communicate with existing devices, it cannot be efficiently utilized. For example, it is inconvenient that every time a new device is introduced, all the devices to be connected to the new device must be changed.